Not owned by Paramount
Paramount do not own the rights to tbis film. It was produced solely by Aubrey Schenck Productions Inc. Paramount merely distributed the film in 1964; they negotiated the rights for the VHS in 80s/90s. Criterion would have negotiated with Aubrey Schenck (and Paramount?) for their Laserdisc release. Aubrey Schenck died in 1999. So, much like Cornell Wilde's, The Naked Prey, this film is not owned by Paramount currently, but by the films' original, independent film company/individual rights owner. Paramount probably do not care about this, as it would be too much like hard work to them and would, of course, entail them paying money to make money with the DVD release, that may not be a big enough seller in their eyes. With that said, Paramount will probably be the holders of the original 35mm camera negatives, interpositives and sound elements, so even if a third party was to try and release a DVD, they would have to negotiate with Paramount (or sue them) for use of the prime 35mm film and sound elements; otherwise, they would have to use an old print held by Aubrey Schenck's Estate.
Sorry to bring you down, but these are facts and the reasons for the lack of DVD for the popular film that has been demanded on DVD for that last six years.
"We forfeit three-fourths of ourselves in order to be like other people." - Arthur Schopenhauer